The current networks are based on a point-to-point architecture, where all channels are converted to an electrical format (optical-to-electrical-to-optical or OEO) for traffic switching, aggregation and regeneration.
With the evolution of the optical devices, it is now possible to extend the optical reach and to provide the network nodes with optical passthrough. For example, U.S. Pat. No. 5,751,454 (MacDonald et al.) discloses OADM (optical add/drop multiplexer) node configurations with wavelength bypass in optical format. Such a node is equipped with an optical demultiplexer that separates the WDM signal (multi-channel signal) on the input line into drop channels and passthrough channels; the drop channels are routed to a respective local user, and the passthrough channels are routed to the output of the node. At the output side of a node, an optical multiplexer combines the passthrough channels with the locally generated channels (add channels) into the output line.
Also, tunable optical devices are now coming onto the market. Thus, for example Nortel Networks announced general availability for a widely tunable laser ML-20 for use in optical transmitters (Tx). Tunable filters that select a certain wavelength can be used at the receiving side, so that a broadband receiver (Rx) using such filters may detect any channel. JDS Uniphase Corporation manufactures a blocker, which can block a set of channels (one or more channels that need not be consecutive) than can be dynamically reconfigured.
A new generation of all optical networks is emerging, driven by customer demand for individualized classes of service, with the corresponding revenue differentiation. This new generation of networks will enable the customers with the ability to automatically establish end-to-end connections at a push of a button. This means that the nodes of the network need to be able to switch the traffic in optical domain, while automatically regenerating the signal only when necessary. This approach dramatically reduces the node complexity, and consequently the network cost.
Optical networks may be classified according to the area they serve; relevant to this invention are the metro networks and long-haul (or core, or transport) networks. U.S. Pat. No. 6,084,694 (Milton et al.) illustrates examples of metro rings with optical passthrough, where any two nodes around the ring may be connected using pre-selected bands of wavelengths. Nonetheless, the wavelength allocation to each connection is fixed for an entire band of channels, which reduces the flexibility of operation.
US patent application identified above as U.S. patent application Ser. No. 09/876,391 describes an agile core (transport, long-haul) optical network that uses optical switching and a scalable and flexible architecture for end-to-end (rather than point-to-point) routing/switching of channels. This patent application is incorporated herein by reference.
Typically, metro network aggregate capacities are lower than those in long haul networks. Also, connection capacities are lower; metro optical networks operate at 2.5 Gb/s rates or lower, while long-haul networks use 10 Gb/s per wavelength. Thus, to interconnect traffic from metro into long-haul networks, a multiplexing or aggregation function must be fulfilled to map finer granularity metro connections into higher rate long-haul connections. The aggregation may be circuit-based TDM (time division multiplexing) or packet-based aggregation. Ideally, the interconnection must enable also switching of the metro channels into the correct higher rate long-haul channel. These aggregation and switching functions are typically achieved with an electrical switch fabric that interconnects long-haul and metro transponders
There is an opportunity to extend the agility of a agile core network into a metro network, to provide wavelength routing capability right out to the customer premise. This could be achieved by enabling the nodes (edges) of the metro network with full tunability. However, this solution may be currently cost prohibitive.